Such a device is known from WO 01/85434 of applicant. This known device can be used for instance for sealing bags manufactured from foil material tight, after these have been inflated with air or a different suitable filling medium. The thus obtained bags can be used as, for instance, filling material in packages, for the protection of products included in these packages. The known device comprises a sealing block provided with a sealing thread, and a counter block arranged opposite this sealing block, provided on a side facing the sealing block with a layer of resilient material. This ensures that a sealing force, applied by the counter block, is evenly distributed over the foil material to be sealed, so that an even sealing seam is obtained, of constant quality. Further, two Teflon circulating belts are provided, which are guided along the sealing surfaces facing each other of the sealing block and counter block, and between which, in use, the foil material is carried along. These circulating belts prevent direct contact between, on the one side, the foil material and, on the other side, the sealing block with the sealing thread and the counter block with the resilient layer, so that adhesion between the parts mentioned is prevented.
A drawback of this device is that between the resilient layer and the circulating belt guided therealong, considerable frictional forces can occur, which leads to wear. Furthermore, this may slow the circulating belt down, so that speed differences with respect to the other belt are formed. This leads to irregular pulling forces to the foil material, as a result of which this may begin to crease or deform otherwise, resulting in deformed sealing seams. Further, as a rule, resilient materials have a limited heat conduction coefficient or a great insulating action. With a device according to the invention, this causes heat given off by the sealing thread to be retained between the sealing block and the counter block, at least being insufficiently discharged, so that the sealing temperature rises and is difficult to control. This is unfavourable to the sealing quality.